Consumable electrode arc welding method and consumable electrode arc welding device

ABSTRACT

If a short circuit does not occur during deceleration of a wire feed speed in forward feed of a welding wire before the wire feed speed reaches a predetermined wire feed speed, a cyclic change is stopped and the wire feed speed is constantly controlled at the first feed speed. If a short circuit occurs during forward feed at the first feed speed, deceleration from the first feed speed starts, and the cyclic change is resumed for welding. This achieves uniform weld bead without increasing spatters even if any external disturbance such as change of distance between a tip and base material occurs.

This application is a divisional of U.S. patent application Ser. No.13/000,779, filed Dec. 22, 2010, which is a U.S. National PhaseApplication of PCT International Application PCT/JP2010/003991, filedJun. 16, 2010, the entire disclosures of which are incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to consumable electrode arc weldingmethods and consumable electrode arc welding devices that feed a weldingwire, which is a consumable electrode, and welds the wire onto aworkpiece to be welded by alternately generating a short circuit stateand an arc condition between the consumable electrode and the workpiece.

BACKGROUND ART

Demand for faster welding speed and less spatter, so as to increaseproductivity, have been increasing in the welding industry. Fasterwelding speed increases production quantity per time, and thus weldingproductivity increases. Less spattering reduces a post-treatment processof removing spatter attached to a base material, and thus weldingproductivity also increases.

FIG. 5 shows waveforms of wire feed speed Wf, welding voltage Vw, andwelding current Aw in conventional arc welding. First, conventional arcwelding is described with reference to FIG. 5. In a known weldingprocess, the wire feed speed is changed cyclically to forcibly cause ashort circuit, and arc is re-generated by forcibly opening the shortcircuit (for example, refer to Patent Literature 1). In this prior art,the short circuit is opened without depending on electromagnetic pinchforce of welding current, and thus spatter can be reduced.

In FIG. 5, time T1 is one time point in an arc period while arc isgenerated between a wire end and a base material. Wire feed speed Wfaccelerates toward maximum speed Wf2.

At time T2, the wire and the base material are short-circuited, and ashort circuit period starts. Wire feed speed Wf is controlledcyclically, regardless of an arc condition, according to a predeterminedcommand value. Accordingly, a short-circuit timing may be a time pointother than when wire feed speed Wf is at maximum speed Wf2. Theshort-circuit timing is a time point when the wire feed speed is aroundthe maximum speed Wf2. It may be a time point during forwardacceleration or forward deceleration. The timing differs with everyshort circuit.

Time T3, at which the short circuit is opened and arc is regenerated,comes during backward feed. A short-circuit opening timing may be a timepoint other than when wire feed speed Wf is at minimum speed (Wf4). Theshort-circuit opening timing is a time point when the wire feed speed isaround minimum speed Wf4. It may be a time point during backwarddeceleration or backward acceleration. The timing differs with everyshort-circuit opening. At any timing, however, the short circuit isopened during backward feed. Accordingly, the short circuit is forciblyopened without depending on electromagnetic pinch force of weldingcurrent, and thus spatter can be reduced.

Wire feed speed Wf includes one forward feed and one backward feed inits one cycle. In one cycle, one short circuit and one opening of shortcircuit take place. In response to this cyclic operation of wire feedspeed Wf, welding involving arc phenomenon is controlled. Apredetermined cycle of wire feed speed Wf is a short-circuit generatingfrequency or the number of short circuits per second. This stabilizeswelding while reducing spatter.

With respect to a welding device in which the wire is controlled to feedforward and backward, there is disclosed a welding control method ofcontrolling the wire feed speed in response to welding phenomenon. (Forexample, refer to Patent Literature 2.) The wire feed speed isaccelerated during the arc period, and is then controlled at apredetermined constant speed. When a short circuit is detected, the wirefeed speed is decelerated, and then the wire is drawn up at apredetermined constant speed different from the above constant speed toopen the short circuit and regenerate arc. Welding takes place throughrepetition of these operations. Also in this method, the short circuitis opened during backward feed. Accordingly, the short circuit isforcibly opened without depending on the electromagnetic pinch force ofwelding current, and thus spatter can be reduced.

In the aforementioned conventional welding control method disclosed inPatent Literature 1, stable welding with less spatter is achievable ifthere is no disturbance such as change of distance between the tip andbase material. However, for example, if the position of base materialdeviates and the distance from the tip becomes longer during welding,the distance between the tip and base material becomes suddenly longerat timing A shown in FIG. 5. When this extended distance becomes greaterthan a distance advanced in the forward feed period of the wire feedspeed, a short circuit does not occur. Then, the process goes on tobackward feed in this state, which means the state without short circuitcontinues. Accordingly, generation of short circuit is delayed until thenext forward feed period (e.g., until time T4). During this periodwithout generation of short circuit, a droplet is formed at the wireend, and this droplet grows. A large droplet is released from the wireend by the movement of wire due to the change of distance between thetip and base material. This may become spatter and may splatter out of aweld pool. Even if the droplet does not splatter outside, a largedroplet extends the short circuit state. The short circuit may not besufficiently opened in the next short circuit, and thus the droplet mayadhere to the base material. As a result, the state of unstable arc hasoccurred.

As shown in FIG. 6, let's say a short circuit occurs at time T5, anddistance between the tip and base material becomes suddenly shorter attiming B. If this shortened distance becomes greater than a length ofwire drawn up at the wire feed speed in the backward feed period, theshort circuit continues without being opened until the next backwardfeed period (e.g., until time T6). In this case, temperature of a weldedportion decreases, and weld bead narrows and thins due to extended shortcircuit time. This may result in uneven bead width. In addition, weldingmay become not feasible due to deposited wire end and base material.Alternatively, if a high current of about 400 A to 500 A is continuouslyapplied, a short-circuiting wire portion may splatter by generating alarge amount of spatter by means of electromagnetic pinch force, and arcmay be regenerated. In any case, spatter generation increases, and thebead width becomes uneven.

In the welding device, in which the wire is controlled to feed forwardand backward, disclosed in Patent Literature 2, the cycle of forwardfeed and backward feed of the wire feed speed is controlled in responseto the arc phenomenon in the conventional welding control method forcontrolling the wire feed speed in line with the welding phenomenon.Accordingly, if the short circuit time becomes longer, the backward feedbecomes longer. If the arc time becomes longer, the forward feed becomeslonger. Opposite states are also controlled in the same way. The averagefeed speed of wire feed speed, short circuit cycle, and the number ofshort circuits become unstable and change if the arc phenomenon changes.Welding results thus cannot be stabilized.

If there is almost no change in the distance between the tip and basematerial, there is no problem. However, external disturbance such aschange of distance between the tip and base material typically due todeviation in placement of base material or variations in accuracy ofcomponents, such as pressed components, frequently occur at actualproduction sites. Accordingly, the average feed speed of wire feed speedand short circuit cycle greatly change and fluctuate, resulting indifficulty to stabilize welding results.

-   Patent Literature 1: Japanese Patent Unexamined Publication No.    S62-6775-   Patent Literature 2: Japanese Patent Examined Publication No.    S48-11463

SUMMARY OF THE INVENTION

A consumable electrode arc welding method of the present invention is aconsumable electrode arc welding method in which welding takes place ata wire feed speed that cyclically changes between forward feed forfeeding toward a workpiece and backward feed for feeding in a directionopposite to the forward feed in a predetermined cycle and amplitude. Ifa short circuit does not occur during deceleration of wire feed speed inthe forward feed of the welding wire before the wire feed speed reachesa predetermined wire feed speed, before a predetermined time passes fromarc generation, or before a feed cycle of welding wire reaches apredetermined angle when a predetermined feed cycle of welding wire isexpressed by an angle; the cyclic change of wire feed speed is stoppedand the speed is constantly controlled at the first feed speed. If ashort circuit occurs during forward feed at the first feed speed,deceleration from the first feed speed starts, and the cyclic change isresumed for welding.

The consumable electrode arc welding method of the present invention isa consumable electrode arc welding method in which welding takes placeat a wire feed speed that cyclically changes between forward feed forfeeding toward a workpiece and backward feed for feeding in a directionopposite to the forward feed in a predetermined cycle and amplitude. Ifa short circuit is not opened during acceleration of wire feed speed inbackward feed of the welding wire before the wire feed speed reaches apredetermined wire feed speed, before a predetermined time passes fromshort circuit generation, or before a feed cycle of welding wire reachesa predetermined angle when a predetermined feed cycle of welding wire isexpressed by an angle; the cyclic change of wire feed speed is stoppedand the speed is constantly controlled at the second feed speed. If ashort circuit is opened during backward feed at the second feed speed,acceleration from the second feed speed starts, and the cyclic change isresumed for welding.

A consumable electrode arc welding device of the present invention is anarc welding device in which welding takes place by repetition of the arcstate and short circuit state between the welding wire and workpiece.The arc welding device includes a switching element for controllingwelding output; a welding voltage detector for detecting weldingvoltage; a welding condition setting unit for setting current; a shortcircuit/arc detector for detecting the short circuit state and arc statebased on an output of the welding voltage detector; a memory for storingthe set current, average feed speed of wire feed speed, frequency ofwire feed speed, and amplitude of wire feed speed in a linked manner; awire feed speed determinator for determining the average feed speed ofwire feed speed, frequency of wire feed speed, and amplitude of wirefeed speed from the memory based on the set current set by the weldingcondition setting unit; and a wire feed speed controller for controllingcyclic change of forward feed and backward feed of the wire feed speedby receiving the output of the short circuit/arc detector and the outputof the wire feed speed determinator. The wire feed speed controllerstops a cyclic change of the wire feed speed and applies constantcontrol at the first feed speed if a short circuit does not occur duringdeceleration of wire feed speed in forward feed of the welding wirebefore the wire feed speed reaches a predetermined wire feed speed,before a predetermined time passes from arc generation, or before a feedcycle of welding wire reaches a predetermined angle when a predeterminedfeed cycle of welding wire is expressed by an angle. If a short circuitoccurs during forward feed at the first feed speed, deceleration fromthe first feed speed starts, and the cyclic change of wire feed speed isresumed for welding.

The consumable electrode arc welding device of the present invention isan arc welding device in which welding takes place by repetition of thearc state and short circuit state between the welding wire andworkpiece. The arc welding device includes a switching element forcontrolling welding output; a welding voltage detector for detectingwelding voltage; a welding condition setting unit for setting current; ashort circuit/arc detector for detecting the short circuit state and arcstate based on an output of the welding voltage detector; a memory forstoring the set current, average feed speed of wire feed speed,frequency of wire feed speed, and amplitude of wire feed speed in alinked manner; a wire feed speed determinator for determining theaverage feed speed of wire feed speed, frequency of wire feed speed, andamplitude of wire feed speed from the memory based on the set currentset by the welding condition setting unit; and a wire feed speedcontroller for controlling cyclic change of forward feed and backwardfeed of the wire feed speed in a cycle by receiving the output of theshort circuit/arc detector and the output of the wire feed speeddeterminator. The wire feed speed controller stops a cyclic change ofthe wire feed speed and applies constant control at the second feedspeed if a short circuit is not opened during acceleration of wire feedspeed in backward feed of the welding wire before the wire feed speedreaches a predetermined wire feed speed, before a predetermined timepasses from arc generation, or before a feed cycle of welding wirereaches a predetermined angle when a predetermined feed cycle of weldingwire is expressed by an angle. If a short circuit is opened duringbackward feed at the second feed speed, acceleration from the secondfeed speed starts, and the cyclic change of wire feed speed is resumedfor welding.

With the above structure, spatter can be reduced and uniform bead can beachieved by controlling the wire feed speed, even if any externaldisturbance, such as change of distance between the tip and basematerial, occurs during arc generation. Accordingly, stability of arccan be enhanced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an arc welding device in accordancewith first to third exemplary embodiments of the present invention.

FIG. 2 illustrates waveforms of a wire feed speed, welding voltage, andwelding current in accordance with the first exemplary embodiment of thepresent invention.

FIG. 3 illustrates waveforms of a wire feed speed, welding voltage, andwelding current in accordance with the second exemplary embodiment ofthe present invention.

FIG. 4 illustrates a waveform of a wire feed speed, welding voltage, andwelding current in accordance with the third exemplary embodiment of thepresent invention.

FIG. 5 illustrates waveforms of a wire feed speed, welding voltage, andwelding current in conventional arc welding.

FIG. 6 illustrates waveforms of a wire feed speed, welding voltage, andwelding current in conventional arc welding.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are described below withreference to FIGS. 1 to 4.

First Exemplary Embodiment

FIG. 1 is a schematic diagram of an arc welding device in this exemplaryembodiment. FIG. 2 shows waveforms of a wire feed speed, weldingvoltage, and welding current when welding takes place adopting aconsumable electrode arc welding control method in this exemplaryembodiment.

In FIG. 1, input AC voltage from input power supply 1 is applied towelding power supply 14, and is rectified by primary rectifying element3. Switching element 4 switches and controls an output of primaryrectifying element 3 to an output appropriate for welding, and maintransformer 2 converts the input power supply to an output appropriatefor welding. Secondary rectifying element 6 rectifies one of secondaryoutputs insulated from the primary side in main transformer 2, andreactor 5 smoothes it to a current appropriate for welding. The currentsmoothed by reactor 5 is applied to torch 18 via one welding poweroutput terminal 14 a. The other secondary output of main transformer 2is connected to base material 15 via welding current detector 8 thatdetects welding current and also via other welding power output terminal14 b.

Welding voltage detector 9 for detecting welding voltage is connectedbetween welding power output terminals 14 a and 14 b. Wire 16 is fedfrom wire storage 25 to tip 20 attached to torch 18 by wire feeder 19controlled by wire feed speed controller 13 that controls the wire feedspeed. Wire 16 is used as a consumable electrode. Arc 17 is generatedfrom an end of wire 16 to base material 15 by the welding power supplyoutput. Short circuit/arc detector 10 determines whether a welding stateis a short circuit state in which wire 16 and base material 15 aremaking contact, or an arc state in which a short circuit is opened andarc is generated, based on a welding voltage detection signal fromwelding voltage detector 9 connected to short circuit/arc detector 10.This determination is input to output controller 11 and wire feed speedcontroller 13.

Welding condition setting unit 12 outputs welding conditions (setwelding current and set welding voltage) set by an operator to outputcontroller 11 that controls the welding output and wire feed speedcontroller 13. Detection signals of welding current detector 8 andwelding voltage detector 9 are input to output controller 11. Memory 21and wire feed speed determinator 22 in wire feed speed controller 13 aredescribed later.

FIG. 2 shows waveforms illustrating changes by time of welding voltageVw that is welding output voltage and welding current Aw that is weldingoutput current. In FIG. 2, when wire feed speed Wf is positive, itindicates that the wire is fed forward to base material 15. When wirefeed speed Wf is negative, wire 16 is fed away from base material 15. Inother words, it means wire 16 is drawn up in backward feed.

Time t1 shown in FIG. 2 is within the arc period where arc is generated.Outputs of welding voltage Vw and welding current Aw are controlled toform an appropriate droplet in order to smoothly transfer the droplet atthe wire end in a coming short circuit period. Wire feed speed Wfchanges cyclically according to a predetermined command value(amplitude, frequency, and average feed speed) regardless of the arccondition (short circuit period or arc period). At time t1, wire 16 isfed forward in an accelerated manner. In FIG. 2, acceleration is adirection that the wire feed speed changes from the peak of backwardfeed to the peak of forward feed. Deceleration is a direction that thewire feed speed changes from the peak of forward feed to the peak ofbackward feed. The peak of forward feed in the wire feed speed ismaximum speed Wf2, and the peak of backward feed in the wire feed speedis minimum speed Wf4 in the description.

In the short circuit period from time t2 to t3, welding current Awreduces from time t2, which is an initial point of short circuit, bycontrolling the current, so as to ensure generation of short circuit.Then, welding current Aw is increased in a predetermined slope. On theother hand, the wire is fed in a predetermined cycle of wire feed speedWf, and wire feed speed Wf changes from the acceleration period todeceleration period regardless of the arc condition. If this cycle ofwire feed speed Wf is between 30 to 100 Hz, there is no problem. Wirefeed speed Wf decelerates and transfers from forward feed to backwardfeed in the short circuit period from time t2 to time t3. Then, at timet3, when backward feed starts, the short circuit is forcibly opened, andarc is regenerated.

In the output control during the arc period, starting from time t3,there is a higher tendency that higher peak current IP of weldingcurrent Aw penetrates into the weld pool deeper due to higher arcconvergence, typically in CO₂ welding. In the worst case, the basematerial may melt off. On the other hand, if peak current IP is too low,a faint short circuit may occur. Accordingly, peak current IP needs tobe set to minimum necessary welding current Aw in order to avoidgeneration of faint short circuit and also prevent penetration of weldpool. An appropriate value for this peak current IP is obtainedtypically through experiments depending on a workpiece to be welded.

During the arc period on and after time t3, a short circuit occurs inthe forward feed of wire feed speed Wf if there is no disturbance andthe distance between the tip and base material is constant. However, ifany disturbance, such as longer distance between the tip and basematerial due to a deviated placement position of base material away fromthe tip end, occurs at time A, the arc period continues withoutoccurrence of short circuit. Therefore, in this exemplary embodiment,the welding wire is fed cyclically according to the predeterminedcommand value for wire feed speed Wf, and the speed accelerates up tomaximum speed Wf2 during forward feed. Then, deceleration starts duringforward feed. If the short circuit does not occur even if the speed isreduced to first feed speed Wf1, which is the predetermined wire feedspeed, deceleration is stopped and switched to the control of feedingthe welding wire at a constant value of first feed speed Wf1. This firstfeed speed Wf1 is wire feed speed Wf in forward feed for feeding weldingwire 16 toward base material 15. Accordingly, a short circuit willcertainly occur as time passes. Accordingly, backward feed does notstart without a short circuit, which was a disadvantage of the priorart. A droplet at the wire end will not grow and thus spatter will notincrease.

A short circuit can be generated earlier by setting this first feedspeed Wf to the average feed speed set corresponding to each set weldingcurrent or faster than the average. To cause short circuit at earliertiming, higher first feed speed Wf1 is better. However, first feed speedWf1 is preferably not as high as maximum speed Wf2. This is because ifthe distance between the tip and base material is constant when nodisturbance occurs, a short circuit is generated at timing when wirefeed speed Wf is around maximum speed Wf2 (within about ±⅛ cycle).Therefore, a short circuit may occur after deceleration starts frommaximum speed Wf2.

If the distance between tip and base material is constant, there isalmost no influence on opening of short circuit even if the timing ofshort circuit deviates around maximum speed Wf2 for about ±⅛ cycle.Therefore, the welding wire can be just cyclically fed at wire feedspeed Wf according to the predetermined command value. However, forexample, if a value of first feed speed Wf1 and a value of maximum speedWf2 are set to the same value, all wire feed speeds Wf after the timingthat a short circuit occurs at maximum speed Wf2 may be controlled to aconstant value. This will disturb the cycle of wire feed speed Wf. Thisdisturbance of cycle leads to variations in the cyclic nature ofgeneration and opening of short circuit or the number of short circuits.Welding results thus become unstable.

If a short circuit is not generated, the feed speed is preferablycontrolled to a constant value roughly between the average feed speedset for each set welding current and an intermediate speed of maximumspeed Wf2 of amplitude (speed at a point ⅛ cycle after maximum speedWf2). In other words, if the feed speed controlled at a constant valueis between the average feed speed and the speed at a time point ⅛ cycleafter maximum speed Wf2, the cycle of wire feed speed Wf will not bedisturbed. If the feed speed controlled to a constant value is out ofthis range, a cycle of wire feed speed Wf will be disturbed.

If a short circuit occurs at time t4, deceleration of wire feed speed Wfis resumed from the control at constant value (first feed speed Wf1).The predetermined cyclic wire feed speed is resumed. On and after timet4, the feed speed decelerates, and soon feeding changes from forwardfeed to backward feed. At time t5, the short circuit is opened, and arcis regenerated.

With this operation, a droplet at the wire end will not grow by changingwire feeding from forward feed to backward feed, even if generation of ashort circuit is delayed due to longer distance between the tip and basematerial at timing A. In addition, a short circuit can be generatedearlier compared to the case of not setting a constant value to wirefeed speed Wf. Disturbance of short-circuit cycle, in line withreduction of spatter generation and longer short circuit period, issuppressed. Stability of arc can thus be enhanced. The consumableelectrode arc welding control method in this exemplary embodimentrepeats the above cycle of short circuit period and arc period.

Next is described an arc welding device for the aforementioned controlof consumable electrode arc welding with reference to FIG. 1. In FIG. 1,welding voltage detector 9 is connected between welding power outputterminals 14 a and 14 b, and outputs a signal corresponding to detectedvoltage. Short circuit/arc detector 10 determines whether weld outputvoltage Vw is less or not less than a constant value based on the signalfrom welding voltage detector 9. Based on this determination result, theshort circuit state, in which wire 16 is making contact and generatingshort circuit with base material 15 that is a workpiece, or the arcstate, in which wire 16 is not making contact, is determined and adetermination signal is output.

Next is described the wire feed control after short circuit/arc detector10 makes determination. Wire feed speed controller 13 outputs to wirefeeder 19 a signal for controlling the speed at predetermined cyclicwire feed speed Wf, so as to control wire feed speed Wf. This cyclicwaveform may be sinusoidal, as shown in FIG. 2, or trapezoidal as longas cyclic form is achieved. Wire feed speed controller 13 includesmemory 21 that stores a formula or table including set current, averagefeed speed of wire feed speed Wf, frequency of wire feed speed, andamplitude of wire feed speed Wf in a linked manner; and wire feed speeddeterminator 22 that determines the average feed speed of wire feedspeed Wf, frequency of wire feed speed Wf, and amplitude of wire feedspeed Wf with reference to memory 21 based on the set current set inwelding condition setting unit 12. In this way, wire feed speedcontroller 13 controls wire feeding by outputting to wire feeder 19 asignal that repetitively controls the cycle of forward feed and backwardfeed of wire feed speed Wf upon receiving an output of short circuit/arcdetector 10 and an output of wire feed speed determinator 22.

Next is described, the welding output control of welding current Aw andwelding voltage Vw. Output controller 11 outputs a signal forcontrolling welding current or welding voltage with reference to anappropriate parameter for the short circuit period, in case of the shortcircuit period, based on a weld waveform parameter selected depending onthe set welding current and set welding current set by an operator viawelding condition setting unit 12. In case of arc period, outputcontroller 11 outputs a signal for controlling welding current orwelding voltage with reference to an appropriate parameter for the arcperiod. These output signals are input to switching element 4 to controlthe welding output.

Now, the operation is described below when the distance between the tipand base material becomes longer, which is external disturbance, in thearc period. If wire feed speed controller 13 does not receive a signalindicating generation of short circuit from short circuit/arc detector10 before the wire feed speed is decelerated to predetermined first feedspeed Wf1 in forward feed, as shown FIG. 2, during the decelerationperiod in forward wire feed, wire feed speed controller 13 suspends thepredetermined cyclic deceleration control, and switches from the cycliccontrol to the constant-value control at first feed speed Wf1. Wire feedspeed controller 13 outputs a control signal to wire feeder 19 to feedwire 16 at a constant speed. This constant wire feeding at first feedspeed Wf1 continues until a short circuit is generated and wire feedspeed controller 13 receives a short-circuit detection signal from shortcircuit/arc detector 10.

Since first feed speed Wf1 is a predetermined forward feed value, shortcircuit is soon generated. Wire feed speed controller 13 thus receivesthe short-circuit detection signal from short circuit/arc detector 10.Then, wire feed speed controller 13 switches from the constant-valuecontrol at first feed speed Wf1 to the predetermined cyclic control, andthe cyclic control is resumed to restart deceleration based on a cyclicspeed command. Output controller 11 appropriately controls weldingcurrent and welding voltage in the short circuit period until the shortcircuit is opened.

In this exemplary embodiment, a value for waiting generation of shortcircuit, i.e., timing to stop changing wire feed speed Wf cyclically andswitching to the constant-value control at first feed speed Wf1, is setto timing when the wire feed speed becomes first feed speed Wf1.However, a predetermined angle (e.g., 110° if an angle of first feedspeed Wf1 is 90°) may be set when one cycle of wire feed speed is angleof 360°. Wire feed speed Wf may be controlled to change from cyclic wirefeed speed Wf to constant speed if short circuit is not generated beforethis angle. Alternatively, a value for waiting generation of shortcircuit, i.e., timing to stop changing wire feed speed Wf cyclically,may be a time point when a predetermined time passes from opening theshort circuit or a time point when a predetermined time passes from atime point at which the wire feed speed reaches first feed speed Wf1.

As described above, in this exemplary embodiment, a droplet at the wireend does not grow by backward feed of wire 16 even if generation of ashort circuit is delayed due to external disturbance such as extendeddistance between the tip and base material in the deceleration period atforward wire feed speed during arc generation. And, early generation ofa short circuit can be encouraged during forward feed. Accordingly, theexemplary embodiment can better stabilize arc by reducing spattergeneration, and suppressing variations in the short circuit cycle andthe number of short circuits due to extended interval between shortcircuits.

Second Exemplary Embodiment

Parts that are same as the first exemplary embodiment are given the samereference marks to omit duplicate detailed description in this exemplaryembodiment. Major difference from the first exemplary embodiment is thecontrol of wire feed speed Wf when arc is not generated during backwardwire feed in the short circuit period between generation of shortcircuit and generation of arc.

FIG. 1 used in the first exemplary embodiment shows a schematic diagramof a consumable electrode arc welding device also applicable to thisexemplary embodiment. FIG. 3 shows waveforms of a wire feed speed,welding voltage, and welding current when welding takes place adopting aconsumable electrode arc welding control method in this exemplaryembodiment.

Time t1 in FIG. 3 is within the arc period where arc is generated.Outputs of welding voltage Vw and welding current Aw are controlled toform an appropriate droplet in order to smoothly transfer the droplet ata wire end in a coming short circuit period. Wire feed speed Wf iscontrolled cyclically according to a predetermined command value. Thewire feed speed is accelerated at time t1.

In the short circuit period from time t2 to time t3, the wire is fedaccording to the predetermined command value, and outputs of weldingcurrent Aw and welding voltage Vw are appropriately controlled in theshort circuit period. The output control is the same as that describedin the first exemplary embodiment. Then, at time t3, the short circuitis opened, and arc is regenerated. In this way, welding takes place byrepetition of generation of short circuit and regeneration of arc.

At time t4, a short circuit occurs again. Wire 16 is fed cyclicallyaccording to the predetermined command value, and outputs of weldingcurrent Aw and welding voltage Vw are appropriately controlled in theshort circuit period. However, let's say external disturbance such as ashorter distance between tip 20 and base material 15 occurs at timing Bin this short circuit period, typically due to positional deviation inplacement of base material 15 that is a workpiece, and base material 15becomes closer to an end of tip 20. In this case, the short circuitcontinues without being opened.

In this exemplary embodiment, acceleration is stopped and wire 16 is fedat a constant value of second feed speed Wf3, so as to suppresscontinuation of short circuit without being opened, if the short circuitis not opened at a time point when the wire feed speed reaches secondfeed speed Wf3 during acceleration from minimum speed Wf4 in backwardfeed. Since second feed speed Wf3 is a value for backward feed, the wirecan be certainly drawn up to open the short circuit. Accordingly, thisexemplary embodiment can suppress splattering of wire portion, increasedspatter, or adhesion of the wire end and base material that may occurduring short-circuiting if the process moves onto forward feed withoutopening the short circuit, as described in a disadvantage of the priorart.

Timing for opening a short circuit can be made earlier by setting alower value (higher in a negative absolute value) for second feed speedWf3. Accordingly, lower second feed speed Wf3 is better for earliertiming of opening the short circuit. However, second feed speed Wf3 ispreferably not as low as minimum speed (Wf4). This is because if thedistance between the tip and base material is constant when nodisturbance occurs, the short circuit is opened at timing when a valueof wire feed speed Wf is around minimum speed Wf4 (roughly within ±⅛cycle). Therefore, the short circuit may be often opened afteracceleration starts from minimum speed Wf4.

If the distance between the tip and base material is constant, there isno influence on generation of next short circuit or a short-circuitcycle even if the timing of short circuit deviates around minimum speedWf4 (for about ±⅛ cycle). Therefore, there will be no problem if thewire is fed cyclically at wire feed speed Wf according to thepredetermined command value. However, for example, if a value of secondfeed speed Wf3 is set to the same value as minimum speed Wf4, the wirefeed speed will be controlled to a constant value to open the shortcircuit in all cases when the short circuit is opened at timings afterminimum speed Wf4. This will disturb the cycle of wire feed speed. Thisdisturbance of cycle leads to variations in the cyclic nature ofgeneration and opening of short circuit, or the number of shortcircuits. Welding results thus become unstable. Accordingly, a thresholdwire feed speed for controlling the feed speed to the constant valuewhen the short circuit is not opened is preferably set to the wire feedspeed at the time point roughly about ⅛ cycle after minimum feed speedWf 4.

If the short circuit is opened at time t5, wire feed speed Wf isswitched from the constant-value control at second feed speed Wf3 to thecyclic control. The acceleration control is then resumed, and thepredetermined cyclic wire feed speed is resumed. Since the wire feedspeed is accelerated, wire feeding transfers from backward feed toforward feed as time passes, and a short circuit is generated.

The above control suppresses adhesion of the wire end and base materialor splatter and causes early opening of the short circuit even ifopening of the short circuit is delayed due to shorter distance betweenthe tip and base material at timing B. Accordingly, stability of arc canbe enhanced by reducing spatter generation and also reducing disturbanceof the short-circuit cycle.

The consumable electrode arc welding control method in this exemplaryembodiment repeats the above cycle of short circuit period and arcperiod.

Next is described, with reference to FIG. 1, an arc welding device forthe aforementioned control of consumable electrode arc welding when adistance between the tip and base material becomes shorter during theshort circuit period. As shown in FIG. 3, wire feed speed controller 13switches the wire feed speed from predetermined cyclic accelerationcontrol to constant-value control at second feed speed Wf3, and outputsthis control to wire feeder 19 when a short-circuit opening signal isnot input from short circuit/arc detector 10 before acceleration of thewire feed speed reaches second feed speed Wf3 in backward feed. Theconstant feed control at second feed speed Wf3 is then applied until theshort circuit is opened.

Since second feed speed Wf3 is a predetermined backward feed value, theshort circuit is soon opened, and wire feed speed controller 13 receivesan opening detection signal from short circuit/arc detector 10. Wirefeed speed controller 13 then resumes the acceleration control of wirefeed speed Wf4 according to the predetermined cyclic speed command fromthe constant-value control at second feed speed Wf3. In the arc period,output controller 11 controls welding current and welding voltageappropriate for the arc period until next generation of short circuit.

In this exemplary embodiment, a value for waiting opening of shortcircuit, i.e., timing to stop changing cyclic wire feed speed Wf, is setat second feed speed Wf3. However, a predetermined angle (e.g. 300° ifan angle of minimum speed Wf4 is 270°) may be set when one cycle of wirefeed speed is an angle of 360°. Alternatively, a value for waitingopening of short circuit, i.e., timing to stop changing the wire feedspeed cyclically, may be a time point when a predetermined time passesfrom occurrence of short circuit, or a time point when a predeterminedtime passes from the time point at which the wire feed speed reachesminimum speed Wf4.

As described above, the consumable electrode arc welding device and theconsumable electrode arc welding control method in this exemplaryembodiment can prevent adhesion of the wire end and base material,suppresses splatter, and encourages early opening of short circuit evenif opening of short circuit is delayed due to shorter distance betweenthe tip and base material in the acceleration period at the backwardwire feed speed. This reduces spatter generation and also reducesvariations in the short circuit cycle and number of short circuits.Accordingly, stability of arc can be enhanced.

Third Exemplary Embodiment

Parts that are same as the first and second exemplary embodiments aregiven the same reference marks to omit duplicate detailed description.Major difference from the first and second exemplary embodiments is thecontrol of wire feed speed to achieve a predetermined average wire feedspeed for each set welding current by calculating an average wire feedspeed for every cycle of cyclic wire feed speed.

FIG. 1 used in the first and second exemplary embodiments show astructure also applicable to a consumable electrode arc welding devicein this exemplary embodiment. FIG. 4 shows waveforms of a wire feedspeed and average feed speed when welding takes place adopting theconsumable electrode arc welding control method in this exemplaryembodiment.

A dotted line of Wfs1 in FIG. 4 shows a reference average feed speedthat is set for each set welding current. As described later, this isset based on set current. Reference average feed speed Wfs1 is preset tothat equivalent to an average value of cyclically changing wire feedspeed.

To respond to unexpected external disturbance, such as change ofdistance between the tip and base material, in the middle of welding, asdescribed in the first and second exemplary embodiments, a cyclic changeof wire feed speed is stopped, and wire feeding is controlled at aconstant speed different from the cyclic wire feed speed. This changesthe average value of wire feed speed, and the average feed speed becomesdifferent from aforementioned reference average feed speed set for eachset welding current.

For example, external disturbance has not occurred until a time point oftime t6 in FIG. 4. The wire is thus fed cyclically at the predeterminedcyclic wire feed speed. The average wire feed speed until time t6 isequivalent to reference average feed speed Wfs1. However, externaldisturbance shown in the first exemplary embodiment occurs in the nextcycle (from time t6 to t7). If the feed control described in the firstexemplary embodiment is executed, time for controlling the wire feedspeed at a constant value of first feed speed Wf4 until a short circuitoccurs increases, and an average wire feed speed for one cycle from timet6 to t7 becomes Wfo1, which is ΔWf1 higher than reference average feedspeed Wfs1. An increase of the average feed speed increases wire feedamount, and this increased feeding is ΔWf1×Δt1 against preset wire feedamount. This increased feed amount increases weld amount, and thus beadwidth broadens and bead height becomes taller. Amount of weldpenetration also increases. If external disturbance further continuesand the number of increases continue, the wire weld amount furtherincreases, and the bead width, bead height, or penetration depthincreases. This may cause burn-through, giving detrimental effect onwelding results.

To suppress this detrimental effect, an average of the wire feed speedis controlled and set to predetermined reference average feed speed Wfs1from time t7 so that the aforementioned increase in the wire feed speedin the next cycle (Δt2) can be balanced. More specifically, the wirefeed speed in the next one cycle (Δt2) is set to the feed speed shiftedin parallel to the lower-speed direction so that the average wire feedspeed becomes Wfs2 obtained by subtracting ΔWf2 (=(ΔWf1×Δt1)/Δt2), whichis the increase divided by the time of next one cycle, frompredetermined reference average feed speed Wfs1. The wire feed speed iscontrolled by shifting in parallel the average feed speed, i.e., thecenter position of amplitude, to the lower-speed direction withoutchanging the amplitude and frequency.

With this control, even if the average wire feed speed increases to thepredetermined reference average wire feed speed due to temporal changeof wire feed speed against external disturbance, this increase can bebalanced in the next one cycle, and the speed returns to thepredetermined reference average wire feed speed. Accordingly, thewelding results are not affected, and satisfactory weld bead can beachieved.

Contrary, if the average wire feed speed decreases due to a shorterdistance between the tip and base material, as shown in the secondexemplary embodiment, the wire feed speed in the next one cycle isincreased to balance the decrease.

If the increase or decrease is too large to balance only by the next onecycle, the increase or decrease may be balanced using multiple cycles,such as two cycles or three cycles.

As described above, this exemplary embodiment controls the average wirefeed speed of wire feed speed to the predetermined reference averagewire feed speed in the next cycle or the next multiple cycles even ifthe average feed speed of the wire feed speed is changed to reduce anyincrease in spatter generation or unstable arc due to unexpectedexternal disturbance occurred in the middle of welding, as described inthe first and second exemplary embodiments. Accordingly, any effect onthe bead width, bead height, or penetration depth can be suppressed.

INDUSTRIAL APPLICABILITY

The arc welding control method and device of the present invention canreduce spatter and improve stability of arc by controlling the wire feedspeed even if external disturbance such as change of distance betweenthe tip and base material occurs during welding. Accordingly, thepresent invention is industrially effective to methods and devices forarc welding that successively feeds the welding wire that is aconsumable electrode.

REFERENCE MARKS IN THE DRAWINGS

-   -   1 Input power supply    -   2 Main transformer    -   3 Primary rectifying element    -   4 Switching element    -   5 Reactor    -   6 Secondary rectifying element    -   8 Welding current detector    -   9 Welding voltage detector    -   10 Short circuit/arc detector    -   11 Output controller    -   12 Welding condition setting unit    -   13 Wire feed speed controller    -   14 Welding power supply    -   14 a, 14 b Welding power output terminal    -   15 Base material    -   16 Wire    -   17 Arc    -   18 Torch    -   19 Wire feeder    -   20 Tip    -   21 Memory    -   22 Wire feed speed determinator    -   25 Wire storage

What is claimed:
 1. An arc welding device in which welding takes placeby repeating an arc state and a short circuit state between a consumablewelding wire and a workpiece to be welded, the device comprising: aswitching element for controlling current output by said welding device;a welding voltage detector for detecting a welding voltage; a weldingcondition setting unit for setting a set current; a short circuit/arcdetector for detecting one of the short circuit state and the arc statebased on an output of the welding voltage detector; a memory for storingthe set current, an average feed speed of wire feed speed of theconsumable welding wire, frequency of the wire feed speed, and anamplitude of the wire feed speed in a linked manner; a wire feed speeddeterminator for determining the average feed speed of wire feed speed,the frequency of wire feed speed, and the amplitude of wire feed speedfrom the memory based on the set current set by the welding conditionsetting unit; and a wire feed speed controller for receiving an outputof the short circuit/arc detector and an output of the wire feed, speeddeterminator, and controlling the wire feed speed as the consumablewelding wire feed transitions between forward feed and backward feed,wherein the wire feed speed controller starts a constant control of thewire feed speed at a second constant feed speed, and the constantcontrol is started when a short circuit is not opened duringacceleration of the wire feed speed in the backward feed before one of:the wire feed speed reaching a predetermined feed speed; a predeterminedtime passing from short circuit generation; and a feed cycle of theconsumable welding wire reaching a predetermined angle when one feedcycle of the consumable welding wire is expressed by angle.
 2. The arcwelding device of claim 1, wherein the wire feed speed controllercalculates an average cyclic wire feed speed of a cycle for each cycle;if the average cyclic wire feed speed of one cycle is lower than anaverage wire feed speed, welding takes place at the wire feed speedshifted in parallel to more than the average wire feed speed so that theaverage cyclic wire feed speed of a cycle on and after a next cycle ofthe one cycle becomes higher than the average wire feed speed, the wirefeed speed being an average cyclic wire feed speed on and after the nextcycle; and if the average cyclic wire feed speed of the one cycle ishigher than the average wire feed speed, welding takes place at the wirefeed speed shifted in parallel to a lower speed than the average wirefeed so that the average cyclic wire feed speed of the cycle on andafter the next cycle of the one cycle becomes lower than the averagewire feed speed, the wire feed speed being the average cyclic wire feedspeed on and after the next cycle.
 3. The arc welding device of claim 2,wherein the cycle on and after the next cycle is a next one cycle. 4.The arc welding device of claim 3, wherein acceleration from the secondconstant feed speed starts when the short circuit is opened during thebackward feed at the second constant feed speed.
 5. The arc weldingdevice of claim 2, wherein the cycle on and after the next cycle is aplurality of cycles on and after the next cycle.
 6. The arc weldingdevice of claim 5, wherein acceleration from the second constant feedspeed starts when the short circuit is opened during the backward feedat the second constant feed speed.
 7. The arc welding device of claim 2,wherein acceleration from the second constant feed speed starts when theshort circuit is opened during the backward feed at the second constantfeed speed.
 8. The arc welding device of claim 1, wherein thepredetermined wire feed speed is the second feed speed.
 9. The arcwelding device of claim 8, wherein acceleration from the second constantfeed speed starts when the short circuit is opened during the backwardfeed at the second constant feed speed.
 10. The arc welding device ofclaim 1, wherein the wire feed translations between forward feed andbackward feed are one of a sinusoidal and trapezoidal translations. 11.The arc welding device of claim 10, wherein acceleration from the secondconstant feed speed starts when the short circuit is opened during thebackward feed at the second constant feed speed.
 12. The arc weldingdevice of claim 1, wherein the wire feed speed is an average wire feedspeed corresponding to a set current.
 13. The arc welding device ofclaim 12, wherein acceleration from the second constant feed speedstarts when the short circuit is opened during the backward feed at thesecond constant feed speed.
 14. The arc welding device of claim 1,wherein acceleration from the second constant feed speed starts when theshort circuit is opened during the backward feed at the second constantfeed speed.
 15. An arc welding device in which welding takes place byrepeating an arc state and a short circuit state between a welding wireand a workpiece to be welded, the device comprising: a switching elementfor controlling current output by said welding device; a welding voltagedetector for detecting a welding voltage; a welding condition settingunit for setting a set current; a short circuit/arc detector fordetecting one of the short circuit state and the arc state based on anoutput of the welding voltage detector; a memory for storing the setcurrent, an average feed speed of wire feed speed, a frequency of thewire feed speed, and an amplitude of the wire feed speed in a linkedmanner; a wire feed speed determinator for determining the average feedspeed of wire feed speed, the frequency of wire feed speed, and theamplitude of wire feed speed from the memory based on the set currentset by the welding condition setting unit; and a wire feed speedcontroller for receiving an output of the short circuit/arc detector andan output of the wire feed speed determinator, and controlling the wirefeed speed as the wire feed transitions between forward feed andbackward feed, wherein the wire feed speed controller starts a constantcontrol of the wire feed speed at a second feed speed if a short circuitis not opened during acceleration of the wire feed speed in the backwardfeed of the welding wire before one of the wire feed speed reaching apredetermined feed speed, a predetermined time passing from shortcircuit generation, and a feed cycle of the welding wire reaching apredetermined angle when one feed cycle of the welding wire is expressedby angle; and if the short circuit is opened during the backward feed atthe second feed speed, acceleration from the second feed speed startsand the transition between forward feed and backward feed is resumed forwelding, and the wire feed translations between forward feed andbackward feed are a sinusoidal translations.
 16. The arc welding deviceof claim 15, wherein the wire feed speed controller calculates anaverage cyclic wire feed speed of a cycle for each cycle; if the averagecyclic wire feed speed of one cycle is lower than an average wire feedspeed, welding takes place at the wire feed speed shifted in parallel tomore than the average wire feed speed so that the average cyclic wirefeed speed of a cycle on and after a next cycle of the one cycle becomeshigher than the average wire feed speed, the wire feed speed being anaverage cyclic wire feed speed on and after the next cycle; and if theaverage cyclic wire feed speed of the one cycle is higher than theaverage wire feed speed, welding takes place at the wire feed speedshifted in parallel to a lower speed than the average wire feed so thatthe average cyclic wire feed speed of the cycle on and after the nextcycle of the one cycle becomes lower than the average wire feed speed,the wire feed speed being the average cyclic wire feed speed on andafter the next cycle.
 17. The arc welding device of claim 16, whereinthe cycle on and after the next cycle is a next one cycle.
 18. The arcwelding device of claim 16, wherein the cycle on and after the nextcycle is a plurality of cycles on and after the next cycle.
 19. The arcwelding device of claim 15, wherein the predetermined wire feed speed isthe first feed speed.
 20. The arc welding device of claim 15, whereinthe wire feed speed is an average wire feed speed corresponding to a setcurrent.